A modern refinery is an integrated complex designed to utilize as much of the crude oil as possible. A distillation tower divides the crude into a plurality of cuts by boiling point range. Depending on the properties of the crude, some of these cuts are usable without further processing. However, most of the streams from the distillation tower are treated to change one or more of its properties. For example, impurities, such as sulfur or nitrogen, are reduced in cuts destined for burning. It is beneficial to increase the octane in cuts that will be used in the gasoline pool. Heavy cuts, which are generally lower in value, can be converted into lighter, more profitable cuts by catalytic cracking. The fluid catalytic cracking unit, or “FCC unit,” for example, converts virgin gas oil to gasoline and light cycle oil.
Further, demand for various petroleum products varies over time. In the summer, gasoline and jet fuel are in demand during the travel season. During the winter, more heating and fuel oil is used than during the warm summer months. Changes in technology often produce a shift in demand for oil products. Thus, it is also important that a refinery be able to vary the relative amounts of the products to meet these changing demands.
Complexities of the refinery often lead to inefficiencies and duplication of units. There are often several hydrotreaters for removal of impurities. The hydrotreaters may operate at different process conditions or using different catalysts depending on the quality or boiling point range of the feedstock. It would be beneficial if at least some of the refinery processes could be combined into an integrated process to more efficiently utilize process equipment available in the refinery.